It is often necessary, in both consumer and commercial contexts, to wait for a water source to reach a suitable temperature prior to use. For example, it is very common for an individual to turn on the hot water in the shower, or at a sink, and then wait for an extended length of time until the water is at the correct temperature.
Additionally, vast amounts of water and energy are wasted each year due to the delay in receiving water at the correct temperature. That is, as most individuals are reluctant to stand by the shower and continuously monitor the water temperature for many minutes, a significant amount of hot water is simply lost down the drain. This increases both water costs as well as heating costs. Multiplied by the number of individuals that must engage in this practice on a daily basis, the waste is significant.